1. Field of the Invention
The present invention relates to an image forming apparatus of the electrophotographic type or electrostatic recording type, such as a copy machine, a multifunction printer and a laser beam printer, for example.
2. Description of the Related Art
The color-image forming apparatus of the electrophotographic type can be further divided into two types: one transfers a toner image directly from an image bearing member to a recording material; and the other transfers a toner image from an image bearing member to an intermediate transfer member in a primary transfer process, and then transfers the toner image from the intermediate transfer member to a recording material in a secondary transfer process.
The color-image forming apparatus of the type of transferring a toner image directly from an image bearing member to a recording material often uses an electrostatic adsorption belt for conveying the recording material, while the color-image forming apparatus of the type of transferring a toner image from an intermediate transfer member to a recording material in the secondary transfer process often uses an intermediate transfer belt.
In general, for the secondary transfer process to transfer a toner image to a recording material, the color-image forming apparatus has a configuration in which, by means of a secondary transfer roller, the recording material is conveyed while the secondary transfer process is being performed with the recording material being held between a secondary transfer opposing roller of the intermediate transfer member and the secondary transfer roller.
Some secondary transfer rollers have a configuration in which a secondary transfer unit that integrally unitizes conveying paths before and after the secondary transfer process together is spaced apart from the intermediate transfer member, thereby enabling the secondary transfer unit to be opened and closed for the clearance of jams of the recording material such as a sheet of paper, the easy replacement of the intermediate transfer member or the unit including the intermediate transfer member and the like.
The secondary transfer roller is required to be capable of applying high pressure on the intermediate transfer member and the secondary transfer opposing roller to achieve a good image quality and to prevent the slip of the recording material during its conveyance in the secondary transfer process.
In addition, for locking (securing) or holding the secondary transfer unit, some color-image forming apparatuses have a configuration in which one or more locking portions are respectively provided on both end sides of the secondary transfer unit outside the recording material conveying area. In some cases, not all the locking portions can be fully locked due to reaction force in response to the high pressure of the secondary transfer roller.
In order to avoid this, some color-image forming apparatuses have a configuration in which detection sensors are respectively provided on all the locking portions, and when incomplete locking of the locking portions is detected, a user is prompted to lock the locking portions again.
As in Japanese Patent Application Laid-Open No. 2010-286658, some color-image forming apparatuses have a configuration in which rolling members of locking portions are locked in synchronization with an openable and closable member with the help of separate leading guides.
However, the above prior techniques have the following problems.
It is expensive to provide detection sensors to all the locking portions for detecting incomplete locking of the locking portions and prompting a user to lock the locking portions again. Additionally, this approach is not desirable in terms of usability, because it requires excessive open-close operation by the user.
For the configuration as shown in Japanese Patent Application Laid-Open No. 2010-286658 in which rolling members of locking portions are locked in synchronization with an openable and closable member with the help of separate leading guides, it is difficult to save space because large space is needed for the movement of the leading guides.